Washington (CNN) -- Both the Federal Aviation Administration and the independent National Transportation Safety Board are investigating an aborted landing by a plane carrying first lady Michelle Obama because it was too close to a military plane ahead, officials announced Wednesday.

Neither plane was in danger in the incident Monday at Andrews Air Force Base, according to both agencies.

"We consider any incident like this a serious incident," Transportation Secretary Ray LaHood said in confirming the FAA review. "It's under investigation, we will get to the bottom of what happened and how it happened, and obviously make sure it doesn't happen again."

Later Wednesday, the FAA said in a statement it will now require supervisory oversight in monitoring flights transporting the vice president or first lady. Such supervision is currently required in monitoring flights carrying the president, the FAA said.

LaHood emphasized that the first lady was never in any danger and said he had yet to hear from either Michelle Obama or the president about it. White House Press Secretary Jay Carney confirmed Wednesday that Jill Biden, the vice president's wife, also was on the plane as she and the first lady returned from a series of media events supporting military families.

The NTSB also is launching a probe into Monday's incident, which occurred "after an air traffic controller had sequenced it too close to another military plane," the agency said in a statement.

According to the NTSB statement, the plane transporting the first lady -- the military version of a Boeing 737 -- "was directed to abort its landing attempt after the required minimum separation between it and a C-17 military aircraft that was landing ahead of it was compromised."

It said the incident involved FAA air traffic controllers at the Potomac TRACON regional radar facility in Virginia and the Andrews tower in Maryland.

The planes -- which were both trying to land -- were three miles apart, when they are supposed to be five miles apart, a senior administration official told CNN. The official added it was believed to be an air traffic controller mistake.

Asked why the separation rules governing plane landings were not followed, LaHood said: "That's what we'll figure out in the investigation."

The FAA said in a statement controllers at the Air Force base instructed an incoming Boeing 737 to perform a "go around" "because the plane did not have the required amount of separation" behind the military plane.

"The aircraft were never in any danger," the agency said.

The landing was briefly aborted and the plane carrying the first lady had to circle, according to the senior administration official.

Obama's plane, known as a C-40, was part of the Air National Guard, not the regular Air Force fleet used by VIPs at Andrews, said Maj. Michelle Lai of the 89th Airlift Wing at Andrews Air Force Base.

The FAA did not want Obama's plane to be caught in the "jet wash" of the C-17 as it landed, Lai said, referring to air turbulence trailing in the wake of the plane's jet engines.

"It's important to know the FAA made the right call and at no time was the first lady's life in danger," Lai said.

When the Potomac TRACON radar facility handed off the plane to the Andrews Air Force Base tower, the planes were three miles apart, a government official told CNN.

"Both facilities knew how far apart they were" at the time of the hand-off, the official said. But the official declined to say why the hand-off occurred.

The TRACON could have slowed Obama's plane down or order it to turn earlier, the official said. Why that wasn't done is under investigation, but "it was a controlled situation," the government official said.